1. Field of the Invention
This invention pertains to envelope printing apparatus. More particularly this invention pertains to a feeding and delivery system for multiple simultaneous printings of envelopes retrofit to use ordinary offset duplicators.
2. Background of the Prior Art
There is a continuing demand for envelope imprinting. Printing may be accomplished, among other ways, by engraving, typesetting and by offset. Offset duplicator production is desirable as it is inexpensive to create a master, set up is rapid, and substantial press runs can be made at low cost. However, several barriers prevent more widespread use of ordinary offset duplicators to print envelopes.
The ordinary envelope, such as the business envelope, otherwise commonly known as a number 10 envelope, has two thicknesses in most portions, but as many as four thicknesses of paper along portions where the flap is sealed, in addition to a further thickening and stiff curvature resulting from the gummed lip. When envelopes are stacked, they do not stack evenly as ordinary paper. Once stacked, they are not likely to maintain their upright position in the stack. This instability results from the relationship of the relatively small width of the envelope to the significantly greater height of the envelope stack. For a stack of, for example, a thousand envelopes, the stack exhibits instability and does not stand up straight. That instability is not present in a stack of, for example, one thousand sheets of 20 weight 81/2".times.11" (21.6 cm..times.28 cm.) paper. The instability of envelope stacks is a result both of the rectangularity of the envelopes and the relationship of the area of the envelope to the height of the stack, in addition to the aforementioned variations in envelope thickness.
Additional problems arise when printing envelopes in multiple colors. A separate print run generally must be made for each color ink (unless additional cylinders) are available in the offset duplicator). Each subsequent run requires that the envelopes to be printed be aligned so that the printing of the subsequent color impression is in registration with the previous print of the first color. This registration requires control over the manner in which the envelopes are fed to the printing path of the printing cylinders.
The feed and delivery systems of ordinary offset duplicators tend to be designed for ordinary flat paper which stacks up evenly. Envelopes, such as the usual number 10 business envelope, may not generally be run on ordinary offset presses without unusual careful and time consuming procedures.
There are offset duplicators that are specifically designed for printing envelopes. However, they are expensive. It is generally not economical to dedicate a special high cost offset duplicator for running printing jobs of envelopes. Consequently, the number of such machines is small and they are not within the means of the typical print shop.
Accordingly, it would be beneficial to provide a relatively low cost apparatus for allowing envelopes to be rapidly printed using an ordinary offset duplicator otherwise designed primarily for printing an ordinary flat rectangular paper.